Start building against Spring WS 3.1.8 snapshots

See gh-38284

Author: wilkinsona

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1868,7 +1868,7 @@ bom {
 			]
 		}
 	}
-	library("Spring WS", "3.1.7") {
+	library("Spring WS", "3.1.8-SNAPSHOT") {
 		considerSnapshots()
 		prohibit {
 			versionRange "[4.0.0-M1,)"